-
#3400 by flux_capacitor on 31 May, 2018 14:48
-
Bd: 280mm
Sd: 150mm
Len: 308mm
Material: 1 oz copper PCB flat end plates, 0.5mm thick frustum
Mode: TE013
Freq: 2.45GHz
Df: 0.813
Ql: 22k
Force: min 11mN or 1gf
Forward pwr: 90Wrf
TT, you said to Mike McCulloch that increasing the length of an EmDrive systematically decreases the force produced. Further you say "TE012 or TE013" but every time you put numbers in you still prefer TE013 mode before TE012 mode. I know Shawyer advised you to go for TE013 in 2015, but as you are aware, for the same wide end diameter and frequency, TE013 implies a longer cavity than its TE012 counterpart. So it seems to me this is rather contradictory. -
#3401 by TheTraveller on 31 May, 2018 14:57
-
Goal here is to make this built very low cost and as simple as possible to replicate. Do hope many 1,000 will replicate it.
Switching to the 100W amplifier does complicate things somewhat. You will need a large battery and a voltage step-down regulator to keep the voltage from falling as the battery discharges. You should look at the Polish build for a good example of this.
I can't remember which forward and reverse power detector you are using, but that will usually require an ADC to function with the computer.
I would also recommend a second computer off the test rig so you can use it to control the first computer via remote desktop. Make sure they use 5G wifi as testing at 2.45Ghz will cause problems with standard wifi. The Polish group used arduino wifi at 900Mhz or so. And remember, even solid state computers have fanless vents to move air. Those need to be taped over.
I am also curious how you plan on impedance matching the antenna as that is not shown on your graphic.
Jamie,
Rf amp is a 100W unit that has inbuilt dual directional coupler plus 31dB attenuator in 1dB steps. Can accept 12 to 28 vdc input as it has onboard switching PSU. Comms are RS485 back to the laptop which also drives the freq gen via a USB port. Both Freq gen and Rf Amp have vendor supplied PC software to monitor and control them. Plus I have a PC program that also can control them and do the lowest VSWR tracking.
The coupler will be able to be moved up and down the frutum side wall and be rotated plus penetration depth adjusted. Experience has shown coupler tuning is best done inside the frustum as external tuners do nothing to fix any issue with the coupler and instead just make the load look nice to the Rf amp.
As stated the laptop, the electronics package plus batteries and the drive will be placed inside their own clear plastic 5 sided boxes that have much higher side walls than the object inside the box, so hot rising air can only move up and not sideways. Well not a lot. Considering using a smoke source to allow air movement to be seen.
Look we are talking about a min 12mN or 1.1g of force, or 120mN/kWrf, ie approx 100x what EW achieved.
A friend who is a keen fisherman is taking me to the fishing tackle store so I can buy a range of different tech fishing lines and using a spring gram scale, will twist up the rotarty test rig, loaded with equivalent book mass, so to measure how many revs can be achieved before the twisting up fishing line generates 1g of back torque. Then once the lowest torque, highest rev line is selected, will then proceed to map the back torque at various rotation points so there is a plot of back torque vs deg of rotation, which will later allow a position corrected dynamic accelerative force to be calculated. -
#3402 by TheTraveller on 31 May, 2018 15:10
-
Bd: 280mm
Sd: 150mm
Len: 308mm
Material: 1 oz copper PCB flat end plates, 0.5mm thick frustum
Mode: TE013
Freq: 2.45GHz
Df: 0.813
Ql: 22k
Force: min 11mN or 1gf
Forward pwr: 90Wrf
TT, you said to Mike McCulloch that increasing the length of an EmDrive systematically decreases the force produced. Further you say "TE012 or TE013" but every time you put numbers in you still prefer TE013 mode before TE012 mode. I know Shawyer advised you to go for TE013 in 2015, but as you are aware, for the same wide end diameter and frequency, TE013 implies a longer cavity than its TE012 counterpart. So it seems to me this is rather contradictory.
Travelling wave transit time between the end plates varies with the cavity length and the integral of the group velocity. What I said to Mike was if the Q is held constant, ie constant 5x TC decay time (5 Qu) / (2 Pi Freq) sec, then the longer the transit time (longer length and/ or slower group velocity due to cavity design variant), the lower the number of transits during the 5x TC fill and decay time, the lower the number of end plate impacts/emission events and the lower the force generated.
With this drive, the dimensions are forced by the selection of the form used to make the frustum. A KISS build is not necessarily the way get achieve optimal force.
Consider a TE011 cavity at say 5GHz yet with the same Qu as a TE013 cavity at 2.45GHz. 1/6 the wavefront transit distance and with the same Q, 6x the number of inelastic (during acceleration) end plate impact / emit events during the 5x TC fill and decay time.
Then consider a TE011 24GHz cavity............. -
#3403 by flux_capacitor on 31 May, 2018 15:47
-
Consider a TE011 cavity at say 5GHz yet with the same Qu as a TE013 cavity at 2.45GHz. 1/6 the wavefront transit distance and with the same Q, 6x the number of inelastic (during acceleration) end plate impact / emit events during the 5x TC fill and decay time.
Then consider a TE011 24GHz cavity.............
You are implying that the higher the frequency, the greater the force. Your hypothesis compares cavities with different frequencies but sharing "the same Q"… yet this ideal situation seems rather impossible in practice, as much larger cavities have higher Q factor than smaller ones, and larger cavities lower the frequency. This is why some people on these boards including myself suggested in a previous thread that if someone involved in this field had enough money, he should build a big L-band thruster like a "church bell" (such as the concept in Shawyer's IAC 2013 conference paper, operating at 900 MHz). So all this is not so simple as when you change one setting, all cursors move with respect to the others, and not necessarily in the right direction. -
#3404 by bmcgaffey20 on 31 May, 2018 17:48
-
Phil (aka TheTraveller),
is there any news about your business related to the emdrive and what about the kiss-thruster project?
Does you have any news to share about it to the public? We are curious about the results.
X-Ray,
A super simple to build KISS thruster is being developed. Based on a commercial flower pot. More details & build pictures once the basic thruster is fabricated. BTW it will have KISS copper pcb flat end plates as per Paul's build.
Public demos of the KISS rotary test rig will be held initially in the UK then in the EU, US, Asia and Australia. The demo road trip is planned for early 2019 with the commercial TRL 9 satellite thruster system release in late 2019. Satellite thruster system is a totally different design and build vs the KISS demo thruster.
Projected build specs (subject to change):
Bd: 280mm
Sd: 150mm
Len: 308mm
Material: 1 oz copper PCB flat end plates, 0.5mm thick frustum
Mode: TE013
Freq: 2.45GHz
Df: 0.813
Ql: 22k
Force: min 11mN or 1gf
Forward pwr: 90Wrf
Rotary acceleration data as attached:
Rotary test rig image as attached (note 100W Rf amp to replace the 8W Rf amp shown)
I'm sure you're a busy individual, but you've been posting about KISS thrusters since 2015 without showing any progress on a build. Got any pictures or data to share?
Goal here is to make this built very low cost and as simple as possible to replicate. Do hope many 1,000 will replicate it. Have seen many very over built cavities that achieved next to nothing because the basic EmDrive design and build guidelines were not followed. Building a 1st cavity is not a place for renvention of the wheel. Nor a place to copy a very low efficiency build.
General Principles for the Successful Design and Manufacture of an EmDrive Thruster
http://www.emdrive.com/GeneralPrinciples.pdf
I'm searching for a desired mandrel on which to form the frustum. Very difficult to do this without an internal form.
Once I find it, can then calc the final dimensions to achieve TE012 or TE013 resonance at a freq the 100W Rf amp can drive.
Then the frustum curve will be cut and the photos will start.
To be quite honest with you sir; your under-estimation of the rest of the world to build a working frustum is insulting. If you think a "cheap and easy way" to break the known laws of physics, is actually the answer to getting people to 'believe' that this device works.... IDK what to tell you or any of your followers. Show us some real, tangible results and data already. At this point I don't think it really matters what it costs to build if you can show a working one. I thought 2017 was supposed to be an interesting year man.... what about 2018? 2019 is coming... I'm still waiting. -
#3405 by Monomorphic on 31 May, 2018 21:41
-
Bd: 280mm
Sd: 150mm
Len: 308mm
Mode: TE013
Freq: 2.45GHz
When I run a sweep from 2.4Ghz to 2.5Ghz using these dimensions, I only find one mode at 2.41Ghz. Interestingly, it is one of those modes that looks like TE01x from one slice, but when we look at the surface currents, we can see that it is TE213 (thanks X_Ray!) instead.
-
#3406 by X_RaY on 01 Jun, 2018 05:08
-
Looks like TE214Bd: 280mm
Sd: 150mm
Len: 308mm
Mode: TE013
Freq: 2.45GHz
When I run a sweep from 2.4Ghz to 2.5Ghz using these dimensions, I only find one mode at 2.41Ghz. Interestingly, it is one of those modes that looks like TE01x from one slice, but when we look at the surface currents, we can see that it is a TM mode instead. -
#3407 by TheTraveller on 01 Jun, 2018 06:28
-
Consider a TE011 cavity at say 5GHz yet with the same Qu as a TE013 cavity at 2.45GHz. 1/6 the wavefront transit distance and with the same Q, 6x the number of inelastic (during acceleration) end plate impact / emit events during the 5x TC fill and decay time.
Then consider a TE011 24GHz cavity.............
You are implying that the higher the frequency, the greater the force. Your hypothesis compares cavities with different frequencies but sharing "the same Q"… yet this ideal situation seems rather impossible in practice, as much larger cavities have higher Q factor than smaller ones, and larger cavities lower the frequency. This is why some people on these boards including myself suggested in a previous thread that if someone involved in this field had enough money, he should build a big L-band thruster like a "church bell" (such as the concept in Shawyer's IAC 2013 conference paper, operating at 900 MHz). So all this is not so simple as when you change one setting, all cursors move with respect to the others, and not necessarily in the right direction.
Freq has nothing directly to do with force. However a cavity designed to operate in TE011 mode at 24GHz will have a very small distance between the end plates and thus the travelling wave will make the trip in a much shorter time than in a TE013 cavity with a length that resonates at 2.45GHz.
Lets take a step or two back and consider TE012 vs TE013 at the same Q. TE012 has a smaller distance between it's end plates than does a TE013 cavity. The travelling waves will transit between the TE012 end plates fasten than in the TE013 cavity. Thus for a fixed decay time of (5 Qu) / (2 Pi Freq) and a faster transit time for the TE012 cavity, it would be shown that the force generated by the shorter TE012 cavity will be greater than the force generated by the longer TE013 cavity.
The SPR force equation N = (2 Qu Pwr Df) / 2 is a simplifed equation and uses Qu as an approximation of the number of end plate travelling wave impacts during (5 Qu) / (2 Pi Freq) seconds. The real SPR force equation is more complex.
You might be interested in this analysis I did of the SPR and Qi force equations which suggests the Qi force equation is based on (2 Qu Pwr) / c, as is the SPR equation, with a similar equation to adjust the force per the ratio of the end plate diameters, which both SPR and Qi do.
-
#3408 by TheTraveller on 01 Jun, 2018 06:40
-
Bd: 280mm
Sd: 150mm
Len: 308mm
Mode: TE013
Freq: 2.45GHz
When I run a sweep from 2.4Ghz to 2.5Ghz using these dimensions, I only find one mode at 2.41Ghz. Interestingly, it is one of those modes that looks like TE01x from one slice, but when we look at the surface currents, we can see that it is a TM mode instead.
Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
Same principal is used to design cantennas.
Is why as you will see, the side wall mounted coupler in the KISS drive can be slid up and down the side wall so to find the ideal 1/4 guide wave point from the big end and achieves really good coupler match to the amp without needing an external tuner.
Roger did something like this for the Flight Thruster as he explains:
https://www.youtube.com/watch?v=KUX8EWxmS3k?t=553
(start time 9:12 if the link opens at the start of the video)
Bottom line is you need to physically tune the coupler to obtain the best match.
Attached image with Roger pointing to the Flight Thruster inbuilt coupler tuner.
-
#3409 by oyzw on 01 Jun, 2018 07:54
-
您的解释非常有价值，我同样认为锁定TE01X模态，需要采用侧壁耦合环天线。Bd: 280mm
Sd: 150mm
Len: 308mm
Mode: TE013
Freq: 2.45GHz
When I run a sweep from 2.4Ghz to 2.5Ghz using these dimensions, I only find one mode at 2.41Ghz. Interestingly, it is one of those modes that looks like TE01x from one slice, but when we look at the surface currents, we can see that it is a TM mode instead.
Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
Same principal is used to design cantennas.
Is why as you will see, the side wall mounted coupler in the KISS drive can be slid up and down the side wall so to find the ideal 1/4 guide wave point from the big end and achieves really good coupler match to the amp without needing an external tuner.
Roger did something like this for the Flight Thruster as he explains:
https://www.youtube.com/watch?v=KUX8EWxmS3k?t=553
(start time 9:12 if the link opens at the start of the video)
Bottom line is you need to physically tune the coupler to obtain the best match.
Attached image with Roger pointing to the Flight Thruster inbuilt coupler tuner. -
#3410 by TheTraveller on 01 Jun, 2018 08:16
-
您的解释非常有价值，我同样认为锁定TE01X模态，需要采用侧壁耦合环天线。Bd: 280mm
Sd: 150mm
Len: 308mm
Mode: TE013
Freq: 2.45GHz
When I run a sweep from 2.4Ghz to 2.5Ghz using these dimensions, I only find one mode at 2.41Ghz. Interestingly, it is one of those modes that looks like TE01x from one slice, but when we look at the surface currents, we can see that it is a TM mode instead.
Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
Same principal is used to design cantennas.
Is why as you will see, the side wall mounted coupler in the KISS drive can be slid up and down the side wall so to find the ideal 1/4 guide wave point from the big end and achieves really good coupler match to the amp without needing an external tuner.
Roger did something like this for the Flight Thruster as he explains:
https://www.youtube.com/watch?v=KUX8EWxmS3k?t=553
(start time 9:12 if the link opens at the start of the video)
Bottom line is you need to physically tune the coupler to obtain the best match.
Attached image with Roger pointing to the Flight Thruster inbuilt coupler tuner.
"Your explanation is very valuable. I also think that locking the TE01X mode requires the use of a side-coupled loop antenna."
For ease of replication, will 1st try a 1/4 wave stub antenna being 1/4 the excited resonant wavelength, which at 2.45GHz is 30.55mm. As Rf input power is low and the E field intensity at the big end lobe is the lowest of the lobes, hopefully the end of the stub antenna sticking into the big end E field lobe will not turn into a match.
Then it needs to be placed on the side wall at 1/4 guide wavelength from the big end, which needs simulation as the tapered cavity generates a continually varying guide wavelength and is why it needs to be able to be slid along the side wall so to find the optimal 1/4 guide wavelength spacing from the big end position as simulations are never good enough. -
#3411 by Monomorphic on 01 Jun, 2018 11:50
-
Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
I have very little doubt that TE013 is being excited with the circular antenna at the small end because simulations show that it is TE013. Also, when adjusting the screws on the small end, the RL trace moves up and down - which generally means the cavity is resonating, not the system. The microwaves reflect off the small end and destructively interfere with the waves reflecting off the big end. This also requires moving the antenna up and down along the Z axis to find the best spot.
-
#3412 by flux_capacitor on 01 Jun, 2018 11:56
-
Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
I have very little doubt that TE013 is being excited with the circular antenna at the small end because simulations show that it is TE013. Also, when adjusting the screws on the small end, the RL trace moves up and down - which generally means the cavity is resonating, not the system. The microwaves reflect off the small end and destructively interfere with the waves reflecting off the big end. This also requires moving the antenna up and down along the Z axis to find the best spot.
Jamie, may it be possible that your antenna placement in the middle of the small end works well with your own cavity (i.e. it indeed triggers a resonant TE013 mode) but not with some other aspect ratios like the cavity design just presented by TT (as you didn't find any TE013 mode with this cavity in a 2.4–2.5GHz sweep simulation for the antenna located at small end axis)? -
#3413 by Monomorphic on 01 Jun, 2018 12:05
-
Jamie, may it be possible that your antenna placement in the middle of the small end works well with your own cavity (i.e. it indeed triggers a resonant TE013 mode) but not with some other aspect ratios like the cavity design just presented by TT (as you didn't find any TE013 mode with this cavity in a 2.4–2.5GHz sweep simulation for the antenna located at small end axis)?
It's possible and it is a simple matter to change the antenna type and location and run another sweep. We tried 1/4 wave stub and loop antennas on the sidewall long ago and it didn't seem to make any difference except the stub will excite different modes than the loop. So with TT's newest dimensions and at 2.45Ghz the wavelength is 12.236cm. 1/4 wavelength is 3.06cm from the big end. That is where I will place the antenna.
-
#3414 by TheTraveller on 01 Jun, 2018 12:50
-
Jamie, may it be possible that your antenna placement in the middle of the small end works well with your own cavity (i.e. it indeed triggers a resonant TE013 mode) but not with some other aspect ratios like the cavity design just presented by TT (as you didn't find any TE013 mode with this cavity in a 2.4–2.5GHz sweep simulation for the antenna located at small end axis)?
It's possible and it is a simple matter to change the antenna type and location and run another sweep. We tried 1/4 wave stub and loop antennas on the sidewall long ago and it didn't seem to make any difference except the stub will excite different modes than the loop. So with TT's newest dimensions and at 2.45Ghz the wavelength is 12.236cm. 1/4 wavelength is 3.06cm from the big end. That is where I will place the antenna.
Jamie,
The coupler needs to be 1/4 guide wavelength from the big end plate and not 1/4 excitation wavelength from the big end plate. As the guide wavelength alters as the cavity diameter alters, it is not a straight forward measurement. Which is why the coupler Rf connector needs to be designed into a sliding arrangement that can be moved toward and away from the big end to optimise coupler efficiency and lowest VSWR without needing nor using an external 3 pot tuner.
Plus you may need to bend the antenna a bit and move it in and out a bit to get an even better position and coupler efficiency.
BTW it is altering guide wavelength, smaller with larger diameter and longer with smaller diameter, that causes the small end 1/2 wave to be longer than the big end 1/2 wave.
-
#3415 by flux_capacitor on 01 Jun, 2018 13:24
-
The antenna placement discussion is interesting. But speaking of Shawyer and replication:
Look we are talking about a min 12mN or 1.1g of force, or 120mN/kWrf, ie approx 100x what EW achieved.
The main problem with Shawyer's EmDrive (besides his own theory, as his working principles are rejected by almost all physicists) is that Shawyer doesn't allow any proper IV&V.
Take Woodward's Mach Effect Thrusters for example, now called MEGA (Mach Effect Gravity Assist) drives. Completely different story (again, besides the fact Woodward has a sound working theory and tests his models in a vacuum). Woodward and his team build test articles in California, and they ship them to independent labs, e.g. George Hathaway in Toronto, Canada; and in Europe: Nembo Buldrini in Wiener Neustadt, Austria; and Martin Tajmar in Dresden, Germany… so they can test these thrusters with their own sensitive balance test rigs.
A recent Mach Effect Thruster or MEGA drive built by Jim Woodward.
Before being enclosed in a mu-metal box and tested in a vacuum.
All Shawyer had to do is to ship from UK a "Flight Thruster" presented in the video (a ten-year-old model that according to him produces 100× to 300× the thrust of the Eagleworks Brady cavity) to Martin Tajmar in Germany. Even an older SPR model with flat end plates could have done the trick.
An EmDrive (the "Flight Thruster" 2008 version) presented by Roger Shawyer.
There is no good reason he refused and still refuses to do so. NDAs, etc. are nothing but red herrings that do not hold anymore for old models, especially when Shawyer is able to show some of these old thrusters on TV; that 2008 contracts and export licences have expired; and the tech nowadays is said to be based on more advanced superconducting "2nd gen" thrusters. Therefore, unlike Woodward, this behavior looks like a scam.
The timeline is also dubious and reinforces the impression: the EmDrive had been invented a couple of years ago, there would be no issue. But it has been imagined thirty years ago, in 1988 as a cylinder with a dielectric, and 1998 as a truncated cone, and first built in 2001, so this story has been the same for 17 years (and I'm only taking the first prototype as a beginning). The propellantless thrust is not the only thing anomalous with the impossible drive.
"100× to 300× what EW achieved" has been measured (claimed) by only two individuals in the world: Roger Shawyer, and Phil Wilson (TheTraveller). Although TT states that besides his own (unpublished) tests, several other companies have successfully replicated SPR EmDrives, achieved high thrust levels and are on the verge to launch commercial thrusters… they have not published anything, so there is absolutely no evidence. In science, this is equal to something that does not even exist, so these claims can't be taken into account at all, as they could be genuine, gossip or even deceptive. Same for the Chinese announcements in 2017 from Yue Chen at CAST.
There are only three controlled valuable experiments acceptable to date:
- NASA Eagleworks (tiny thrust levels barely above the noise)
- Chinese Northwestern Polytechnical University (first high power positive results later retracted)
- TU Dresden (major flaws in experiments for now)
And that's all. So everything could be thermal or EM interactions.
SPR Ltd. data is rather sparse and Roger Shawyer being the inventor, his thrusters cannot count in the IV&V list.
Everything else has been only claims for a long time, and is still the case for now.
Monomorphic is the only remaining active hope for the future on the front of DIYers, as proven by his frequently updated cavity and test rig, that are both very well built and regularly shared with the community. I hope Michelle Broyles aka SeeShells will resume her work as well, and Paul March aka Star-Drive can start his activities in his own private lab. I still hope that Phil Wilson aka TheTraveller will share pictures and videos of his own EmDrives, even if the wait has been long overdue and keeps going, and the hope is therefore fading away. -
#3416 by TheTraveller on 01 Jun, 2018 14:15
-
I still hope that Phil Wilson aka TheTraveller will share pictures and videos of his own EmDrives, even if the wait has been long overdue and keeps going, and the hope is therefore fading away.
Consider if you will what the effect on you and others will be when you see my KISS drive and KISS rotary test rig spinning round and round?
Plus you and others get to see all the build steps and learn a few not until now revealed critical secrets on how to build an EmDrive that no one had previously considered. Including many so called experts. Any you ask why many failed?
As example that input tuner on the Flight Thruster has been pointed out by myself before. But did any other builder take notice, work to understand why it was there and incorporate it into their build? No. None.
And you question why builders with little or no microwave experience can't build something better than what EW did.
Maybe ask Sonny White why he did not follow the data, abandon the dielectric and explore TE012 mode operation without a dielectric as it was found to have over 3x the specific force as when using the dielectric. Isn't the rule to FOLLOW tHE DATA?
Why did the force direction change? Well in fact it didn't. It followed the end with the shortest 1/2 guide wavelength, fastest group velocity and highest radiation pressure. As per SPR theory.
-
#3417 by X_RaY on 01 Jun, 2018 14:17
-
The Eigen-frequencies of a cavity resonator is given from its dimensions. When a coupler is placed into the cavity its presence can push the resonant frequency a bit, depending on its shape. This effect does not change the Eigen-frequency spectrum much. Different kind of couplers are able to excite a Eigenresonance. Depending on the vectors field generated by the antenna the coupling factor changes. The Loop antenna used by Jamie is of course a good choice to excite TE01p modes, but if there is no Eigen-frequency solution of this kind within the bandwidth there is nothing to excite.Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
I have very little doubt that TE013 is being excited with the circular antenna at the small end because simulations show that it is TE013. Also, when adjusting the screws on the small end, the RL trace moves up and down - which generally means the cavity is resonating, not the system. The microwaves reflect off the small end and destructively interfere with the waves reflecting off the big end. This also requires moving the antenna up and down along the Z axis to find the best spot.
Jamie, may it be possible that your antenna placement in the middle of the small end works well with your own cavity (i.e. it indeed triggers a resonant TE013 mode) but not with some other aspect ratios like the cavity design just presented by TT (as you didn't find any TE013 mode with this cavity in a 2.4–2.5GHz sweep simulation for the antenna located at small end axis)?
For the given dimensions TE012(~2 GHz) and TE013(~2.3 GHz) are much lower in frequency, TE014(~2.65GHz) is above the discussed band between 2.4 GHz and 2.5 GHz -
#3418 by TheTraveller on 01 Jun, 2018 14:30
-
The Eigen-frequencies of a cavity resonator is given from its dimensions. When a coupler is placed into the cavity its presence can push the resonant frequency a bit, depending on its shape. This effect does not change the Eigen-frequency spectrum much. Different kind of couplers are able to excite a Eigenresonance. Depending on the vectors field generated by the antenna the coupling factor changes. The Loop antenna used by Jamie is of course a good choice to excite TE01p modes, but if there is no Eigen-frequency solution of this kind within the bandwidth there is nothing to excite.Jamie I do have a concern about your use of a circular coupler in the middle of the small end plate.
Exciting a cavity needs to generate travelling waves that move in opposite directions. This is normally achieved by using a sidewall coupler where the big end lobe E field strength is the highest. That point is 1/4 guide wave from the big end. As such when the coupler is excited, some of the energy propogates toward the big end being 1/4 guide wave away, gets a 180 deg flip and comes back to the coupler in phase with the exciting freq.
I have very little doubt that TE013 is being excited with the circular antenna at the small end because simulations show that it is TE013. Also, when adjusting the screws on the small end, the RL trace moves up and down - which generally means the cavity is resonating, not the system. The microwaves reflect off the small end and destructively interfere with the waves reflecting off the big end. This also requires moving the antenna up and down along the Z axis to find the best spot.
Jamie, may it be possible that your antenna placement in the middle of the small end works well with your own cavity (i.e. it indeed triggers a resonant TE013 mode) but not with some other aspect ratios like the cavity design just presented by TT (as you didn't find any TE013 mode with this cavity in a 2.4–2.5GHz sweep simulation for the antenna located at small end axis)?
For the given dimensions TE012(~2 GHz) and TE013(~2.3 GHz) are much lower in frequency, TE014(~2.65GHz) is above the discussed band between 2.4 GHz and 2.5 GHz
The small end is only 13MHz above cutoff. Know from experience that neither Feko nor COMSOL properly handle cutoff in a tapered cavity where the small end is very close to cutoff. You may doubt that but it is the case.
When the cavity is built, will share the VNA scan showing there is resonance where it was predicted. Do hope that example will end the unquestionability of the resonance results from Feko and COMSOL when dealing with small ends that are just above cutoff.
There will be a few more unexpected design and build reveals as the build and test process moves forward. You see I have been here before and know the pathway.
It Is Time For The EmDrive To Come Out Of The Dark. -
#3419 by PotomacNeuron on 01 Jun, 2018 14:48
-
TheTraveller, you said you were looking for a bucket with proper dimension. It might be easier to 3-D print one or turn one from a wood log section.